Circuit-to-circuit interconnections in today's digital computers include on-chip wiring, thin-film or ceramic multichip carriers, and printed circuit boards. In all these cases, it is extremely important to fully characterize these structures since their electrical performance will have a direct impact on the machine cycle time. In most high performance computers, logic signals are propagated over systems of coupled transmission lines. For a large class of these, series resistance is the primary loss mechanism, particular so in the high-density thin-film interconnects currently being investigated. As advances in semiconductor technology continue to decrease the risetimes of signals to be propagated on these structures, their transmission-line characteristics need to be accurately known at higher frequencies. For instance, with a pulse risetime of 50 ps the frequency range of interest is from dc up to about 20 GHz.
Described herein is a simple short-pulse technique for completely characterizing the frequency-dependent electrical properties of transmission lines. High-speed pulse measurements have previously been used for characterizing the transfer functions of microwave antennas and monolithic microwave integrated circuits, the dispersion of microstrips and coplanar striplines and to measure the complex dielectric properties of materials. In the method described here, the measured low-frequency capacitances or inductances and the propagation of high-speed pulses are used to determine the frequency dependent complex propagation matrix, the frequency dependent complex impedance matrix and the frequency dependent complex admittance matrix of a system of coupled transmission lines over a wide frequency range.
The new technique has the following important advantages.
If offers a very simple measurement method for verifying complicated three dimensional models of any system of coupled transmission lines used to connect circuits on chip, on modules, on boards, or between frames.
It uses only the measurement of capacitance and/or inductances and the recording of sets of pulse response waveforms on two similar configurations on the sample under test. It does not need any knowledge of the structure cross section or material characteristics.
The results of the technique can be used directly as inputs to transient circuit analysis programs for wiring performance evaluations. This is extremely useful when three dimensional modelling programs are not available or of limited capability, or the structures are too complicated to be analyzed with standard computing power.
The technique measures the complex frequency dependent propagation matrix, (.GAMMA.(f)) the characteristic impedance matrix, (Z.sub.0 (f)) and the characteristic admittance matrix. (Y.sub.0 (f)) over a broad frequency (f) range while many cross sectional modelling programs have serious limitations especially in the transition region between low-to-high frequency of operation.
The technique could be incorporated into any sampling oscilloscope system as a waveform processing tool.
The method is applied to coupled transmission line systems to measure crosstalk on lossy interconnections which is a very difficult task. In this case the mutual capacitances, or mutual inductances, are measured in addition to self-capacitances or self inductances.
This technique can provide feedback about processing influence on material parameters such as dielectric constant; magnitude of loss tangent and its frequency dependence; or metal conductivity all of which determine the functionality of the interconnections.
These and other objects features and advantages will become apparent from the following detailed description and the drawings and claims appended thereto.